Fiber optic cable termination

ABSTRACT

A method is disclosed for making a termination between (a) a fiber optic cable having a centrally positioned optical fiber, a plurality of reinforcement strands positioned about the optical fiber, and a jacket positioned about the reinforcement strands; with (b) an electro-optic component housing having a tubular extension. In accordance with the method of this invention, in the initial step a predetermined length of the outer jacket is removed from the fiber optic cable to expose a length of optical fiber and reinforcement strands. The optical fiber is then inserted into and through a passage in the tubular extension to a point within the component housing and preferably fixed in place. The reinforcement strands are then positioned about the outer diameter surface of the tubular extension so that portions of the outer diameter of the tubular extension are covered with the reinforcement strands and other areas are left exposed. Then an adhesive is placed over the strands, the exposed areas of the tubular extension, and a portion of the jacket remaining on the fiber optic cable. A heat-shrinkable tubing is then positioned over the adhesive. The tubing is then heated causing it to shrink and make adhesive connection of the exposed area of the tubular member, the reinforcement strands, the jacket of the cable, and the heat-shrink tubing.

This is a division of application Ser. No. 785,790, filed Oct. 9, 1985.

This invention relates to a novel fiber optic cable termination and tothe method of forming the termination. More particularly, this inventionis concerned with a fiber optic cable termination for use in securing afiber optic cable to an electro-optic component housing.

BACKGROUND OF THE INVENTION

Electro-optic systems comprised of optical fibers and electro-opticcomponents are used in a wide variety of commercial applications, suchas in telecommunication of data and the like.

The optical fibers which are commonly employed have a relatively smalldiameter core comprised of an optically transparent material and acladding layer of a polymeric material around the outer surface of thecore which acts to inhibit the dissipation of light from the core. Sinceoptical fibers are relatively weak, they are subject to breakage whenstrain is applied to them. In addition, if strain is applied to anoptical fiber within an electro-optic system, the terminal end of theoptical fiber can be forced out of alignment with an electro-opticcomponent, causing the electro-optic system to become inoperative. Theoptical fibers conventionally are protected by being encased in a fiberoptic cable. The most commonly employed type of fiber optic cable has anoptical fiber in the center of the cable, a plurality of reinforcementstrands positioned circumferentially about the optical fiber and alignedwith the length of the optical fiber so as to be capable of relievingstrain on the optical fiber, and an outer jacket disposed over and aboutthe reinforcement strands.

The electro-optic components include many different types of devices,such as light emitters, light detectors, signal repeaters and the like.Many of the electro-optic components are highly sensitive toenvironmental contaminants and are highly susceptible to physicaldamage. To prevent damage to the components the components are sealed inprotective component housings. The component housings are made invarious shaped configurations to accommodate the different types ofdevices but they all include an opening for passage of an optical fiberthrough to the interior of the component housing.

When connecting a fiber optic cable to an electro-optic component, aterminal end of the optical fiber must be precisely aligned with theelectro-optic component packaged in a component housing and secured inposition. The component housing is then preferably hermetically sealedand the remaining portions of the fiber optic cable, that is, thereinforcement strands and the jacket, are trimmed and secured to thecomponent housing with a mechanical fiber optic cable coupler or alength of heat-shrink tubing.

The terminations of the fiber optic cables to the component housingpresent serious production and performance problems. In order for thefiber optic cable to protect the optical fiber from strain, the ends ofthe reinforcement strands must be locked in position so as to absorb anystrain placed on the fiber optic cable. Certain of the suggestionsheretofore made for terminations required a relatively complex series ofsteps and a skilled operator to make an even marginally satisfactorytermination. Other suggestions required special fittings similar tothose used to couple lengths of fiber optic cable together, whichcouplings resulted in the connection being excessively large. The mostserious problem encountered with the suggested methods was that they didnot provide adequate strain relief so as to prevent breakage andmisalignment of the optical fibers with the components.

It would be highly desirable if a method could be provided for making atermination of a fiber optic cable with a component housing, whichtermination would be simple to make, compact and would providesufficient strain relief so as to protect the optical fiber frombreakage and misalignment.

SUMMARY OF THE INVENTION

A method is disclosed for making a termination between (a) a fiber opticcable of the type having a centrally positioned optical fiber, aplurality of reinforcement strands positioned about the optical fiber,and a jacket positioned about the reinforcement strands; and (b) anelectro-optic component housing having a tubular extension. Inaccordance with the method of this invention, a predetermined length ofthe outer jacket is removed from the fiber optic cable to expose alength of optical fiber and lengths of the reinforcement strands. Theoptical fiber is then inserted into and through a passage in the tubularextension to a predetermined position within the component housing andpreferably fixed in place. The plurality of reinforcement strands arethen separated into at least two groups of strands. The groups ofstrands are then positioned about the outer diameter surface of thetubular extension so that certain areas of the outer diameter of thetubular extension are covered with the reinforcement strands and otherareas are left exposed. A layer of adhesive is then placed over thegroups of fibers, the exposed areas of the tubular extension, and aportion of the jacket remaining on the fiber optic cable. A length ofheat-shrink tubing is positioned about the adhesive layer. The tubing isthen heated causing it to shrink in diameter so as to form an adhesiveconnection of the exposed area of the tubular member, the groups of thereinforcement strands, the jacket of the cable, and the heat-shrinktubing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an isometric pictorial illustration of an electro-opticcomponent housing secured to a fiber optic cable with the fiber opticcable termination of this invention.

FIG. 2 is an illustration of a typical electro-optic component housingof the type used in the present invention.

FIG. 3 is a cross-sectional illustration of a fiber optic cable taken asillustrated by the lines and arrows 3--3 on FIG. 1.

FIG. 4 is a cross-sectional illustration of the fiber optic cabletermination of this invention taken as indicated by the lines and arrows4--4 on FIG. 1.

FIG. 5 is a cross-sectional illustration of the completed fiber opticcable termination taken as indicated by the lines and arrows 5--5 onFIG. 1.

FIG. 6 is an illustration of a fiber optic cable having a terminal endportion of the jacket removed and the reinforcement strands separatedinto separate groups.

FIG. 7 is an illustration in cross section showing the position of theoptical fiber and the reinforcement strands with the tubular extensionof the component housing.

FIG. 8 is an illustration of an adhesive-lined heat-shrinkable tubingheld in position with restraining members about the assembly illustratedin FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1 there is illustrated a sealed electro-optic component housing10 secured to a fiber optic cable with the fiber optic cable termination14 of this invention.

The sealed electro-optic component housing 10 shown in FIG. 1 has a lid16 sealed to the component housing 18 and includes an extension 20 whichis hidden from view by the fiber optic cable termination 14.

In FIG. 2 the electro-optic component housing 18 is shown separate fromthe other elements of the structure of FIG. 1. As can best be seen fromFIG. 2, the electro-optic component housing 18 has a main body 22 havingan interior compartment 24 for receiving an electro-optic device (notshown) and a tubular extension 20 projecting away from the main body 22.The main body 22, as illustrated, is box-like in configuration but canbe of any other configurations as required by the shape of theelectro-optic device to be encased in the component housing 18. Thetubular extension 20 is preferably formed as an integral part of thecomponent housing 18 in order to facilitate hermetic sealing of thecomponent housing 18. The tubular extension 20 projects a predetermineddistance outwardly from the main body 22, which distance is sufficientto support an optical fiber 26 and permit a strong adhesive bond to bemade to the tubular extension 20, as will be explained in greater detailbelow. The tubular extension 20 has a passage 28 which extends from thedistal end 30 of the tubular extension 20 to the interior compartment 20of the component housing 18. The tubular extension 20 has a diameterwhich is slightly larger than the diameter of the optical fiber 26. Theouter surface 32 of the tubular extension 20 can be smooth butpreferably is somewhat roughened in order to provide a surface withimproved gripping properties.

The fiber optic cable 12 which is employed in this invention is ofconventional construction of the type generally described above. Asshown best in FIGS. 3 and 6, the fiber optic cable 12 has an opticalfiber 26 in the center thereof which has a core 34 made of glass, atransparent plastic, or another transparent material, and a claddinglayer 36 formed about the outer surface of the core 34. Surrounding theoptical fiber 26 is a plurality of reinforcement strands 38 which aremade of a relatively flexible, strong synthetic material, such as Kevlar(aramid fiber) sold by E. I. DuPont DeNemour and Company. A compliantjacket 40 made of Teflon (tetrafluoroethylene resin) or nylon isdisposed about the reinforcement strands 38 of the fiber optic cable 12.

The initial step in the formation of the fiber optic cable termination14 of this invention is to remove a predetermined length of the jacket40 from a terminal end of the fiber optic cable 12 as shown in FIG. 6.The removal of a portion of the jacket 40 will cause the reinforcementstrands 38 and the optical fiber 26 to be exposed.

The length of the portion of the jacket 40 which is removed should be atleast as long as the length of the tubular extension 20 of the componenthousing 18 and preferably should be somewhat longer so as to expose asufficient length of optical fiber 26 to facilitate proper alignment ofthe optical fiber 26 with the electro-optic device (not shown) packagedin the interior compartment 24 of the component housing 18.

The reinforcement strands 38 which are exposed on removal of the portionof the jacket 40 of the fiber optic cable 26 are separated into at leasttwo groups 42, 44 thereby exposing the optical fiber 26 as illustratedin FIG. 6. The number of groups of reinforcement strands should belimited to no more than four in order to facilitate the fabrication ofthe fiber optic cable termination 14 of this invention. It has beenfound most preferable that the number of groups of reinforcement strandsshould be limited to two groups of approximately equal size as this isthe simplest number to position and optimum results are obtained withthis number of groups. Accordingly, the further description of thisinvention will be limited to the method wherein two groups 42, 44 areemployed.

The optical fiber 26 is inserted into the distal end 30 and through thepassage 28 of the tubular extension 20 and preferably substantially intothe interior compartment 24 of the component housing 18. The terminalend of the optical fiber 26 is then placed in alignment with theelectro-optic device (not shown). Thereafter, the optical fiber 26 isfixed in place by known methods, such as those shown in U.S. Pat. No.4,237,474 of Ladany and U.S. Pat. 4,479,698 of Landis et al., and ahermetic seal (not shown) is preferably formed between the optical fiber26 and the walls of the passage 28.

The groups 42, 44 of reinforcement strands are then positioned about theouter diameter surface 32 in an alternating pattern as shown in FIG. 7.The groups 42, 44 of reinforcement strands should preferably be spacedapart so that about equal size areas of the outer surface 32 of thetubular extension 20 are covered with the groups 42, 44 of thereinforcement strands and the alternating areas 46 of the tubularextension 20 are exposed.

After the groups 42, 44 of reinforcement strands are in position, anadhesive layer 48 and then a length of heat-shrink tubing 50 are appliedabout the groups 42, 44 of the reinforcement strands, the exposed areas46 of the tubular extension 20, and an end portion 52 of the jacket 40remaining on the fiber optic cable 12. The adhesive layer 48 can beapplied by using a liquid adhesive composition or an adhesive in tapeform and then the length of heat-shrink tubing 50 positioned over theadhesive layer 48. It has been found highly preferable, however, to usea commercially available heat-shrink tubing 50 which is supplied with aheat-activatable adhesive layer 48 about the inner surface of theheatshrink tubing 50. The application of the adhesive layer 48 and theheat-shrink tubing 50 can then be made simultaneously in a more precisemanner.

After the heat-shrink tubing 50 is in position, it is preferably held incontact with the exposed areas 46 of the tubular extension 20 by theclamp members 54, 56, as shown in FIG. 8, to prevent migration of groups42, 44 of reinforcement strands over the exposed areas 46 of the tubularextension 20.

The heat-shrink tubing 50 is then heated with, for example, hot air, tocause the heat-shrink tubing 50 to shrink in diameter and also toactivate the adhesive of the adhesive layer 48, if required. As is mostclearly seen in FIGS. 3 and 4, as the heat-shrink tubing shrinks indiameter, it causes adhesive bonds to form between the groups 42, 44 ofthe reinforcement strands and the heat-shrink tubing 50, the exposedareas 46 of the tubular extension 20 and the heat-shrink tubing 50, andalso the jacket 40 of the fiber optic cable 12 and the heat-shrinktubing 50. Accordingly, a fiber optic cable termination 14 is made inwhich all of the elements of the termination are either directly orindirectly secured to each other. The resulting fiber optic cabletermination 14 has been found to be exceptionally, strongly andespecially effective in preventing strain from being applied to theoptical fiber 26 of the fiber optic cable 12.

What is claimed is:
 1. A termination of a fiber optic cable with anelectro-optic component housing wherein:the fiber optic cable includesan optical fiber and a plurality of reinforcement strands aligned aboutthe length of the optical fiber and a jacket positioned about thereinforcement strands except at a terminal end wherein a portion of atleast a predetermined length of the jacket is removed to provide anunjacketed length of the optical fiber and unjacketed lengths ofreinforcement strands; and the electro-optic component housing has aninterior compartment and a tubular extension of said predeterminedlength having an internal passage in communication with the interior ofthe component housing and an outer diameter surface, reinforcementstrand; and said termination being comprised of the unjacketed length offiber positioned within the tubular extension and extending to at leastinterior compartment of the component housing, the unjacketedreinforcement strands being positioned in at least two groups about theouter diameter of the tubular extension to extend the length of thetubular extension in the same direction as the unjacketed fiber so as toleave approximately two portions of the outer diameter of the tubularextension exposed, a layer of adhesive over the groups of unjacketedreinforcement strands, exposed portions of the tubular extension and aportion of the jacket of the fiber optic cable; and, a length ofshrink-fit tubing positioned about the layer of adhesive which tubing isin shrink-fit adhesive engagement with the unjacketed reinforcementstrands, the exposed portions of the tubular extension and the portionof the jacket of the fiber optic cable.